Abrasive article and method of fabrication

ABSTRACT

A continuous elongate flexible sheet bearing erect abrasive flaps, each held by an individual island of binder that is adherently bonded to the flexible support, can be formed into an abrasive flap wheel, endless belts, etc. The article is prepared by applying liquid binder to the sheet, inserting the flaps, isolating the islands, and hardening the binder.

United States Patent McDonald Oct. 24, 1972 [54] ABRASIVE ARTICLE ANDMETHOD [56] References Cited 1 OF gz m i M Donald UNITED STATES PATENTS[72 inventor: W c Sti water Township county of washing, 2,948,090 8/1960Klingspor ..51/337 Minn' Primary Examiner-0thell M. Simpson [73]Assignee: Minnesota Mining and Manufaetur- Attorney-Kinney, Alexander,Sell, Steldt & Delahunt ing Company, Saint Paul, Minn. v 221 Filed:April 30,1971 [57] l h A continuous eongate exib e s eet bearing erect[21] Appl' 139,088 abrasive flaps, each held by an individual island ofbinder that is adherently bonded to the flexible sup- 52 us. Cl 34 1 canbe firmed abrasive flap wheel Int Cl Bub 7 endless belts, etc. Thearticle is prepared by applying [58] Fie'm 51/33L337 358 liquid binderto the sheet, inserting the flaps, isolating 1 the islands, andhardening the binder.

13 Claims, 6 Drawing Figures PATENTED 0m 24 I972 SHEET 1 [IF 2 FIQZINVENTOR. MLL/AM J MCDONALD BY MWAZJZ M ATTORNEYS PATENTEDncr 24 I972 3,699- 727 sum 2 or 2 I N VEN TOR.

6 M L g M J MCDONALD MJWM ABRASIVE ARTICLE AND METHOD OF FABRICATIONThis invention relates to coated abrasives, more particularly to anelongate flap-bearing strip having a continuous array of firmlyanchored, preferably erect, flexible abrasive flaps, and to a method ofmaking the same. The invention also relates to the preparation ofabrasive devices, such as abrasive flap wheels, from such stripmaterials.

Abrasive flap wheels, which comprise an annulus of juxtaposed radiallyextending abrasive flaps or leaves, have been known for a considerableperiod of time. One current method of assembling abrasive flap wheelsinvolves notching opposite edges of the leaves near their base ends sothat when the leaves are arranged in an annular array, the notches formconcentric circular grooves on opposite sides of the array. Reinforcingrings are then seated in the grooves to provide positive anchorage ofthe leaves and to maintain the shape of the annulus. This method isprimarily useful only for the assembly of narrow wheels, and withoutsome other modification would not be suited for the assembly of widewheels.

Rotatable cleaning and polishing brushes have been made withoutrequiring side reinforcement. An early attempt disclosed in U.S. Pat.No. 449,239 involves attaching brush strips to a flexible support bystitching one end of each strip to the support. When mounted on asuitable core and rotated thereon the unattached ends of the strips areforced outwardly by centrifugal force causing flexing or bending of thestrip near its point of attachment. This method however, is notadaptable for use with leaves of coated abrasive sheet materials.Repeated excessive flexing causes the abrasive leaves to weaken and tosubsequently break off before they can be consumed by attrition againsta workpiece, thereby decreasing the useful life of the device.

U.S. Pat. No. 3,468,642 discloses a series of erect abrasive flapshaving one end bonded in a continuous adhesive layer, which may in turnbe bonded to a flexible strip to form an integral structure thatprovides a convenient means of applying the flaps to a rotatable core.The structure as prepared is not capable of providing a flap wheel. Itrequires reinforcing side plates or flanges to complete the wheel.

The flap bearing strip of the invention is simple and easily assembled.It can be easily formed requiring no special skills, into inexpensive,versatile, useful products. Flap wheels formed of the strip require noreinforcing side flanges or plates to provide anchorage of the flaps orto maintain their shape. The flaps of the wheel are not restricted inwidth as is required by some prior art assembly methods; they can beprepared in any desired width.

Briefly, the preferred article of the present invention comprises acontinuous elongate flexible backing sheet or. strip bearing erecttransversely oriented closely spaced abrasive leaves, or flaps. Eachabrasive flap is firmly adherently bonded to a separatesimilarlyoriented narrow elongate island of binder. The islands form what appearsto be a continuous layer of binder when the elongate flap-bearing stripis not flexed or bent, but bending reveals the discontinuities betweenthe segments. The binder islands are closely spaced and adherentlybonded to one major surface of of abrasive leaves. This strip, in anydesired length, can be easily formed into various shapes, e.g., into acircle to provide an annulus of abrasive leaves. The flapbearing stripcan be suitably adhered to a reinforcing member to provide a flap wheelor belt that is ready for use.

Surprisingly, the islands of binder hold the abrasive leaves in place onthe flap wheel without requiring any supplemental reinforcement means.Even after considerable use the abrasive leaves are tenaciously held anderectly supported by the islands. Moreover, the islands appear to reduceadverse flexing or bending within the abrasive leaves that wouldotherwise cause them to prematurely break or tear off. The spacesbetween islands supporting the abrasive leaves permit the flexiblesupport sheet to flex rather than requiring the abrasive leavesthemselves to be severely flexed thereby substantially reducing theabove mentioned flexing and breaking problem.

Articles of the invention can be prepared by applying a continuouscoating of liquid hardenable binder to one surface of the flexiblesupport sheet, inserting the abrasive flaps, isolating correspondingportions of the binder layer to form the islands, and hardening thebinder. Of particular advantage is that the method is adaptable tocontinuous production.

The invention can best be understood and appreciated by reference to theaccompanying drawings wherein like numbers refer to like parts in theseveral views and wherein:

FIG. 1 is a view in perspective showing a segment of a flap-bearingstrip having 'a plurality of erect abrasive leaves or flaps according tothe present invention;

FIGS. 2-4 are fragmentary side views of flap-bearing strips showingvarious ways in which the abrasive leaves can be supported by binderislands;

FIG. 5 is a side view of an abrasive flap wheel embodying the invention;and

FIG. 6 is a side plan view showing a spirally wound abrasive flap wheelalso embodying the invention.

As shown in FIG. 1 the flap-bearing strip 10 of the invention iscomprised of a tough flexible support sheet 15 to which is bondedelongated binder islands 14, each of which holds an abrasive leaf orflap 11 in erect position. The abrasive flaps 11 are held in place bythe binder islands 14 in a face-to-back relation with their abrasivecovered surfaces 13 facing toward the same the flexible sheet, providingan elongated resilient strip end of sheet 15. The strip 10 has a highdegree of bending flexibility, permitting it to be easily formed into anannulus, and a limited degree of twisting flexibility, permitting it tobe spirally wound about a core.

In the embodiment shown in FIG. 1, the islands 14 are bonded to onemajor surface of elongate sheet 15 and extend from side to side. Theislands which support the abrasive flaps have significant thickness andare separate throughout most of the thickness but may be connected by athin binder layer adjacent the flexible support sheet 15.

Each island 14 extends at least the full length of the flap edge whichit is to hold. The island is of sufficient thickness to provide an areawhich will adequately hold the abrasive flap under the most strenuousoperating conditions that may be encountered for use of the flap wheel.Useful for such purpose are islands that are at least one-sixteenth inchin thickness, with the preferred thickness range being fromone-sixteenth to one-fourth inch. The width of island 14, alsosufficient to provide an adequate bonding area, should be at leastone-sixteenth inch, but this may vary upwards depending upon the desirednumber and the thickness of the flaps for each length of theflap-bearing article. Additionally, the islands should not be so wide asto unduly restrict the flexibility of the strip. The islands arenormally made in uniform width to provide uniform spacing of the flaps.For some purposes it may be advantageous to space the islands apart fromeach other, and to have more than one flap per island.

The abrasive leaves or flaps can be any of a multitude of known abrasivemanufactures. Flap 11 comprises a thin rectangular flexible support 12,such as paper, film, or cloth that has abrasive covering one of itsmajor surfaces 13, the abrasive normally being held on the support 12 bya binding medium. Other conventional sheet-like abrasive manufacturescan also provide abra sive flaps; one such material is a sheet-likeabrasive web of randomly oriented polymeric fibers having adjacentfibers bonded together and abrasive particles held thereon by a thincoating of an adhesive material. It is to be noted that although theabrasive flaps 11 are shown in the drawings as being planar, they may besomewhat bowed, due to the curling nature of some abrasive sheets, orthey may be flexible and bent over when not in use. The flaps may alsohave a plurality of parallel slits extending inwardly from their outeredge transforming a single wide flap into rows of finger-like flapswhich more easily conform to the surface of a workpiece. Additionally,it may be desirable to replace some of the abrasive flaps withnon-abrasive flaps to produce special effects such as lubrication of theabrasive flaps, e.g., using a lubricant saturated porous sheet.

The placement of the end of flap 11 with respect to its supportingbinder island can vary in a number of ways. The flap may be bonded toeither of the long edges of the island as shown in FIGS. 2 and 3, or mayactually be embedded within the island and thereby supported on twosurfaces as shown in FIG. 4. The presently preferred method of bondingis that shown in FIG. 2, wherein an area of the surface of flap 11opposite the side coated with abrasive is bonded to binder island 14 andthe entire abrasive coated face 13 of flap 11 is free of such bonding,leaving space 16 between it and the next island. Also useful is thebonding method shown in FIG. 3, wherein the binder is bonded to theabrasive coating leaving space 17 between the opposite surface and thenext island. With this method, however, the bonding of the leaf dependsupon the adhesion of the abrasive coating to the backing, which may notbe sufficient in some cases. Flap 11 may also be held within binderisland 14 as shown in FIG. 4, leaving spaces 18 between islands.Although the method of bonding shown in FIG. 4 produces a superior bond,since flap 11 is bonded on both faces, it requires an additional processstep to prepare, as will be hereinafter described.

Islands 14 can be formed from a number of materials which possess therequired physical properties. The binder must be capable of achieving aliquid state, to permit its application to the surface of sheet 15, andit must be capable of hardening to provide a material that is solid atroom temperature. The binder should adhere to both sheet and flap 11 toprovide an adherent bond between the surfaces. The cured binder shouldhave sufficient internal strength to resist separation when subjected tothe forces encountered in rotation I and use, and sufficient shockresistance to resist fracture upon stopping, starting and encounter witha workpiece. Because flap wheels and other articles of the invention maybe used over an extended period of time while exposed to high workingtemperatures, and because they may be stored in hot warehouses prior touse, it is generally desirable for the binder to retain theaforementioned physical characteristics after being subjected toelevated temperatures, e.g., 150 F. for 24 hours or more.

Suitable binders which provide the aforementioned physicalcharacteristics include those commonly used as bonding resins for coatedabrasive sheet material, such as epoxy resins, hide glue, and phenolicresins, and other known binder materials such as hot melts, polyurethaneresin, polyamide resins, silicone resins, etc.

Flap-bearing strips of the invention can be prepared by placing asupport sheet smoothly along the flat bottom of a trough-like form withrectangular floor and walls that are .capable of holding liquid binderin a depth at least equal to the desired thickness of the binder islandsbeing formed. Liquid hardenable binder is then poured into the form tothe desired depth, flaps inserted thereinto and the binder hardened.

The individual binder islands can be formed in several ways. Thepreferred way involves applying a release coating over one of the majorsurfaces of the flap to prevent adhesion between that surface and thebinder; most preferably the non-adherent material is coated over theabrasive-coated surface. This method will inherently produce islandssuch as are shown in FIGS. 2 and 3, the most preferred producing thatshown in FIG. 2. Upon removal from the form, the finished strip isinitially somewhat rigid clue to slight adherence of the binder to bothsurfaces of the flap. However, flexibility and separation of individualislands is easily accomplished by flexing the strip over a curvedsurface while applying tension to both of its ends.

Another method of forming the flap-bearing strip involves alternatelyplacing non-adherent spacers between abrasive flaps supporting thespacers and flaps in closely adjacent arrangement in a jig, andimmersing one end of each into liquid binder contained in theaforementioned form. Upon hardening of the binder and removal of thenon-adherent spacers, there results a flap bearing strip having binderislands such as is shown in FIG. 4. A flap-bearing strip can be madecontinuously by moving a strip of the flexible support between adjacentside dams moving at the same rate as the support, continuously coatingliquid, hardenable binder on the support, positioning on the side damsclosely spaced flap holding structures, inserting abrasive flaps intothe holding structures from a continuous source, e.g., a

Flap-bearing strip 10 can be formed into various useful abrasive devicessuch as flap wheels 20 or 30 shown in FIGS. 5 and 6 respectively,endless belts, etc. Flap wheel 20 is prepared by forming strip 10 into acircle to produce an annulus of radially extending flaps. The abuttedends of strip 10 are joined by adhesively applying a suitable sheet 21of tough flexible material over the inner surfaces adjacent the edges.Thereafter the annulus is attached to a suitable strongstretch-resistant support member 22. A suitable support member can beprepared by cutting a sheet of stretch-resistant material such as glassfabric, fabric made of glass and strong polymeric fibers (i.e.,polyester), metal mesh, etc., to fit with overlapping ends within theinner curved surface of the annulus, and adhesively applying it therein.Another suitable support member can be provided by a strong tube made ofsuch materials as metal, wood, or cardboard. Generally, wood andcardboard cores are weaker and heavier than the glass fabric core;therefore, they are used for small (i.e., less than two inch innerdiameter) flap wheels.

Flap wheel 30 shown in FIG. 6 has an elongated cylindrical supportmember 31 having spirally wound over and attached to its outer surface asufficient length of the flap-bearing strip of the invention to coverthe entire periphery. This type flap wheel is advantageous for manyapplications because it does not have the edges of its flaps aligned ina perpendicular plane about the axis of the wheel and hence will notproduce streaking or edge marks on workpieces, even when used by themost inexperienced operators.

Another use for the elongate flap-bearing strip includes forming of aflap wheel having inwardly projecting flaps which is useful forfinishing the exteriors of round workpieces such as pipes. Additionally,the strip can be attached to the interior surface of a drum with itsflaps projecting inwardly to provide a tumbling drum thereby eliminatingthe need for loose abrasive particles in such a drum.

To better illustrate the invention, the following nonlimiting examplesare provided wherein all parts and percentages are by weight unlessotherwise stated.

Example 1 A 3-inch wide, approximately 2-inch high, 6-foot longflap-bearing strip having six erect flaps per inch was formed usingflaps of coated abrasive sheet material having glue-starch treateddrills cloth backing, phenolic make and sandsize adhesive, and Grade 80aluminum oxide mineral (sold as 3 Mite coated abrasive sheet). The flapshad been previously roll coated over their abrasive surfaces with a 1.8percent solution of silane resin in organic solvent (Ram Chem. No. 225)to deposit about 0.016 grain of solids per 24 square inches and dried.The flaps were set into a jig having six individual compartments perinch, each compartment being capable of receiving and loosely holdingone flap with its ends exposed. A 4-inch wide, 72-inch long drills clothsheet saturated with a cured mixture of phenolic resin and elastomer(Vinylite XYHL), back-sized with the same mixture filled with powderedcalcium carbonate, and flocked over the front surface with 25 grains/24square inches of 5 denier, 0.055 inch long (ave.) rayon fibers heldthereon by a 12 grain/24 square inches of coating of aphenolzformaldehyde resin, provided the support sheet.

The support sheet was placed with the flocked side up in a previouslyheated aluminum mold assembly having a base part that was 6 feet longand 6 inches wide, having therein a cavity containing a heating elementthat extended its full length. Side dams, 1% inch wide, /fi inch high,and extending the length and width of the base, were placed over theedges of the sheet to hold it smoothly in place, and fastened to thebase portions with screws to provide a trough-like liquid-tight cavity.The inner walls of the side dams were previously coated with a releasecoating.

Fifty grams poly-(oxytetramethylene) glycol endcapped with 2,4-toluenediisocyanate having an equivalent weight of 1,000 (Adiprene" was handmixed in an open container with 8] parts polymethylene polyphenylisocyanate having an equivalent weight of (Mondur MRS), to produce afirst mixture. To the first mixture was added, with stirring, 214 partsof a second mixture consisting essentially of 30 percent4,4'-methylene-bis(2- chloroaniline) (MOCA) in 69.7 percentpolyoxypropylene glycol having an equivalent weight of 1,000 (PPG-2025)and 0.3 percent phenyl mercuric acetate catalyst, to produce a liquidhardenable binder composition.

The liquid hardenable binder composition was uniformly spread in thetrough to a depth of three-sixteenth inch. The jig bearing the flaps wasplaced above the surface of the liquid and supported by its ends on theend side dams, allowing one end of the flaps to fall into the liquidbinder. The immersed ends of the flaps were caused to come into contactwith the support sheet by pressing on their free ends extending abovethe jig. The mold assembly which had been previously heated to F. wasmaintained at that temperature for 30 minutes, causing the binder toharden.

Thereafter the jig was removed and a 6 foot long rigid flap-bearingstrip removed from the mold. The strip was then flexed over a A inchdiameter rod, the islands separating between the silane-coated abrasivesurface and the cured resin to impart flexibility.

A 4 inch inner diameter abrasive flap wheel was prepared by firstcutting a 25.1 inch length of the above described 6 foot strip, trimmingexcess support sheet .from the edges, forming on annulus by abutting itsends, and butt splicing the ends by pressing a 1 inch long, 3 inch widepiece of glass-polyester cloth impregnated with heat curable epoxyadhesive (Epon 828: Versamide 125, 50:50) over the abutted edges andheating to cure the resin. A stretch-resistant core was prepared byfirst cutting a 3 X 27-inch piece of glass-polyester cloth (20 milsthick) and knife coating it with the above-mentioned curable epoxy resinto give a total thickness of 30 mils. The resin-impregnated cloth waspressed against the inner surface of the annulus, held in place on aninflatable core under pressure of 25 psi, and the assembly heated in anair oven at 200 F. for 30 minutes to cure the epoxy resin and producethe completed flap wheel.

The flap wheel was placed on a 4 inch outer diameter expanding mandreland evaluated in a simulated heavy duty grinding operation in which itwas rotated at 4,000 rpm. while being urged at a constant pressure of 5pounds against the surface of a mild steel workpiece. Rotation wasmaintained for a period of 5% hours producing atotal cut of 1,206 gramsof steel (average cut 3.65 grams per minute) with flap wear of 1% inch(average). The wheel performed successfully during the test with no flaploss or excessive vibration. The test was voluntarily terminated afterthe 5% hour period.

EXAMPLE 2-2l To compare a variety of binder materials and flapconstructions, a series of flap wheels was formed from the materialsshown in the table below. Unless otherwise specified the forming steps,the dimensions and the testing of these examples were the same as thosedescribed in Example 1.

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3. The article of claim 1 wherein said binder is polyurethane.

4. The article of claim 1 wherein said abrasive flap comprises a sheethaving abrasive covering one face thereof and said flaps are arranged onsaid abrasive sheet with their abrasive covered faces facing in onedirection.

5. The article of claim 1 wherein said abrasive flap comprises an openporous sheet of randomly oriented polymeric fibers having adjacentfibers bonded together and abrasive particles held therein by a coat ingof adhesive material.

6. An abrasive flap wheel including a length of the abrasive article ofclaim 1 having its ends joined to form an annulus with the flapsradially arranged therefrom, and a tough stretch-resistant supportmember firmly adhesively bonded to the inner surface of said annulus.

7. The abrasive flap wheel of claim 6 wherein said toughstretch-resistant support member is fabric comprised of glass andpolyester fibers.

8. The abrasive flap wheel of claim 6 wherein said support member is arigid tube.

9. The abrasive flap wheel of claim 6 wherein each of said flaps has aplurality of parallel slits starting at the outer end thereof andperpendicular to the axis of rotation of said wheel.

10. A flap wheel including an elongate core having firmly attached tothe outer surface thereof a spirally wound cover comprised of a segmentof the abrasive article of claim 1.

11. A method of fabricating an article having a tough fl 'b1 1 t he tha'n fi dherentl bonded 03 o n 23%;)? urfiace t l'ieiedf z i glurality 0 fclosely spaced parallel transversely oriented narrow islands ofroom-temperature solid binder each of which hold in erect position alike oriented abrasive flap, comprising the steps of:

applying a continuous layer at least one-sixteenth inch in thickness ofliquid hardenable binder upon said one major surface of said sheet;placing erectly supported closely spaced parallel abrasive flaps intocontact with said liquid binder layer; isolating elongate portions ofsaid binder layer to form elongate islands of liquid bindercorresponding to said flaps; and hardening said resin. 12. The method ofclaim 11 wherein said abrasive flaps have a release coating over onemajor. surface.

13. The method of claim 11 wherein said portions of said binder layerare isolated by non-abrasive sheets having releaseable major surfaces.

UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No.3'699'727 p g d October 4,1972

i Invent0r(s) William J- McDonald It is certified that error appears inthe above-identified patent: and that said Letters Patent are herebycorrected as shown below:

Following the Abstract "13 claims should be "14 claims Col. 6 line 37"on" should be "en" Col'. 7, Example 11. "Sic" should .be "SiC" Example14 end of last column "flao wear" should be "flap wear" Footnote 6 l4"should be "140K The following claim inserted 312 Amendment of July 2'7,1972 should be included:

"14. The article of claim 1 wherein each island is firmly adherent'lybonded to and holds in erect position a plurality of like orientedabrasive flaps."

and sealed this let day of May 1973.

QLTLLLLJ if, FLQTCHER, ROBERT GOTTSCI-IAIK Attesbing OfficerCommissioner of Patents CRM PO-lOSO (10-69) USCOMM-DC 60376-P69 U.S.GOVERNMENT PRINHNG OFFICE: l9! 0-366-334

1. An elongate flap-bearing strip comprised of a tough, flexible, elongate support sheet having firmly adherently bonded to and covering one major surface thereof a plurality of closely spaced, parallel, transversely oriented narrow islands of strong room temperature-solid binder each of which is firmly adherently bonded to and holds in erect position, a like oriented abrasive flap.
 2. The article of claim 1 wherein said sheet of tough flexible material is a fibrous sheet.
 3. The article of claim 1 wherein said binder is polyurethane.
 4. The article of claim 1 wherein said abrasive flap comprises a sheet having abrasive covering one face thereof and said flaps are arranged on said abrasive sheet with their abrasive covered faces facing in one direction.
 5. The article of claim 1 wherein said abrasive flap comprises an open porous sheet of randomly oriented polymeric fibers having adjacent fibers bonded together and abrasive particles held therein by a coating of adhesive material.
 6. An abrasive flap wheel including a length of the abrasive article of claim 1 having its ends joined to form an annulus with the flaps radially arranged therefrom, and a tough stretch-resistant support member firmly adhesively bonded to the inner surface of said annulus.
 7. The abrasive flap wheel of claim 6 wherein said tough stretch-resistant support member is fabric comprised of glass and polyester fibers.
 8. The abrasive flap wheel of claim 6 wherein said support member is a rigid tube.
 9. The abrasive flap wheel of claim 6 wherein each of said flaps has a plurality of parallel slits starting at the outer end thereof and perpendicular to the axis of rotation of said wheel.
 10. A flap wheel including an elongate core having firmly attached to the outer surface thereof a spirally wound cover comprised of a segment of the abrasive article of claim
 1. 11. A method of fabricating an article having a tough flexible elongate sheet having firmly adherently bonded over one major surface thereof a plurality of closely spaced parallel transversely oriented narrow islands of room-temperature solid binder each of which hold in erect position a like oriented abrasive flap, comprising the steps of: applying a continuous layer at least one-sixteenth inch in thickness of liquid hardenable binder upon said one major surface of said sheet; placing erectly supported closely spaced parallel abrasive flaps into contact with said liquid binder layer; isolating elongate portions of said binder layer to form elongate islands of liquid binder corresponding to said flaps; and hardening said resin.
 12. The method of claim 11 wherein said abrasive flaps have a release coating over one major surface.
 13. The method of claim 11 wherein said portions of said binder layer are isolated by non-abrasive sheets having releaseable major surfaces. 